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Nuclear Chemistry Unit 2.5.

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Presentation on theme: "Nuclear Chemistry Unit 2.5."— Presentation transcript:

1 Nuclear Chemistry Unit 2.5

2 Introduction to Nuclear Chemistry
Nuclear chemistry is the study of the structure of and the they undergo. atomic nuclei changes

3 Chemical vs. Nuclear Reactions
Chemical Reactions Nuclear Reactions Bonds are broken Nuclei emit particles and/or rays

4 Chemical vs. Nuclear Reactions
Chemical Reactions Nuclear Reactions Bonds are broken Nuclei emit particles and/or rays Atoms are rearranged Atoms changed into atoms of another element

5 Chemical vs. Nuclear Reactions
Chemical Reactions Nuclear Reactions Bonds are broken Nuclei emit particles and/or rays Atoms may be rearranged Atoms changed to atoms of different element Involve valence electrons Involve protons, neutrons, and/or electrons

6 Chemical vs. Nuclear Reactions
Chemical Reactions Nuclear Reactions Bonds are broken Nuclei emit particles and/or rays Atoms are rearranged Atoms change into atoms of different element Involve valence electrons Involve protons, neutrons, and/or electrons Small energy changes Large energy changes

7 Chemical vs. Nuclear Reactions
Chemical Reactions Nuclear Reactions Bonds are broken Nuclei emit particles and/or rays Atoms are rearranged Atoms change into atoms of different element Involve valence electrons Involve protons, neutrons, and/or electrons Small energy changes Large energy changes Reaction rate can be changed. Reaction rate cannot be changed

8 The Discovery of Radioactivity (1895 – 1898):
Roentgen found that invisible rays were emitted when electrons hit the surface of a fluorosent screen (discovered x-rays) Becquerel accidently discovered that phosphorescent rock produced spots on photographic plates uranium

9 The Discovery of Radioactivity (1895 – 1898):
Marie and Pierre Curie isolated the components ( atoms) emitting the rays – process by which atoms give off – the penetrating rays and particles by a radioactive source uranium Radioactivity rays or particles Radiation emitted

10 The Discovery of Radioactivity (1895 – 1898):
Marie Curie, continued polonium identified 2 new elements, and on the basis of their radioactivity These findings Dalton’s theory of indivisible atoms. radium contradicted

11 The Discovery of Radioactivity (1895 – 1898):
Isotopes – atoms of the same element with different numbers of – isotopes of atoms with unstable nuclei (too many or too few neutrons) – when unstable nuclei lose energy by emitting to become more neutrons Radioisotopes Radioactive decay radiation stable Spontaneous Reaction!

12 Alpha radiation Composition – Alpha particles, same as helium nuclei
Symbol – Helium nuclei, He, α Charge – 2+ Mass (amu) – 4 Approximate energy – 5 MeV Penetrating power – low (0.05 mm body tissue) Shielding – paper, clothing 4 2

13 Beta radiation Composition – Beta particles, same as an electron
Symbol – e-, 0-1β Charge – 1- Mass (amu) – 1/1837 (practically 0) Approximate energy – 0.05 – 1 MeV Penetrating power – moderate (4 mm body tissue) Shielding – metal foil

14 Gamma radiation Composition – High-energy electromagnetic radiation
Symbol – ooγ Charge – 0 Mass (amu) – 0 Approximate energy – 1 MeV Penetrating power – high (penetrates body easily) Shielding – lead, concrete

15 Review of Atomic Structure
Nucleus Electron Cloud 99.9% of the mass 1/10,000 the size of the atom 0.01% of the mass 9,999 times the size of the nucleus

16 Review of Atomic Structure
Nucleus Electron Cloud 99.9% of the mass 1/10,000 the size of the atom 0.01% of the mass, 9,999 times the size of the nucleus Protons (p+) and neutrons (n0) Electrons (e-)

17 Review of Atomic Structure
Nucleus Electrons 99.9% of the mass 1/10,000 the size of the atom 0.01% of the mass, 9,999 times the size of the nucleus Protons (p+) and neutrons (n0) Electrons (e-) Positively charged Negatively charged

18 Review of Atomic Structure
Nucleus Electrons 99.9% of the mass 1/10,000 the size of the atom 0.01% of the mass, 9,999 times the size of the nucleus Protons (p+) and neutrons (n0) Electrons (e-) Positively charged Negatively charged Strong nuclear force (holds the protons together) Weak electrostatic force (between electrons and nucleus

19 mass # atomic # neutrons atomic # mass #
Chemical Symbols A chemical symbol looks like… p+ = e- = atomic # To find the number of , subtract the from the mass # 14 C atomic # 6 neutrons atomic # mass #

20 not decompose 1 20 very stable 1:1 p+:n0 6 6
Nuclear Stability not Isotope is completely stable if the nucleus will spontaneously Elements with atomic #s to are . ratio of protons:neutrons ( ) Example: Carbon – 12 has protons and neutrons decompose 1 20 very stable 1:1 p+:n0 6 6

21 21 83 marginally stable 1:1.5 80 120 Nuclear Stability
Elements with atomic #s to are ratio of protons:neutrons (p+ : n0) Example: Mercury – 200 has protons and neutrons marginally stable 1:1.5 80 120

22 > 83 unstable radioactive Uranium Plutonium
Nuclear Stability > 83 unstable Elements with atomic #s are and Examples: and radioactive Uranium Plutonium

23 α He protons +2 mass 4 atomic 2 Atomic number balanced
Alpha Decay α Alpha decay – emission of an alpha particle ( ), denoted by the symbol , because an α has 2 protons and 2 neutrons, just like the He nucleus. Charge is because of the Alpha decay causes the number to decrease by and the number to decrease by . determines the element. All nuclear equations are He 4 2 protons +2 mass 4 atomic 2 Atomic number balanced

24 Alpha Decay Example 1: Write the nuclear equation for the radioactive decay of polonium – 210 by alpha emission. Step 3: Write the alpha particle. Step 4: Determine the other product (ensuring everything is balanced). Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # 210 Po 84 206 Pb 4 He 2 82 Atomic #

25 Alpha Decay Example 2: Write the nuclear equation for the radioactive decay of radium – 226 by alpha emission. Step 3: Write the alpha particle. Step 4: Determine the other product (ensuring everything is balanced). Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # 226 Ra 88 222 Rn 4 He 2 86 Atomic #

26 β electron e- e -1 electron no mass atomic 1
Beta decay β Beta decay – emission of a beta particle ( ), a fast moving , denoted by the symbol or β has insignificant mass ( ) and the charge is because it’s an Beta decay causes change in number and causes the number to increase by . A neutron is converted to a proton and a beta particle. electron e- e -1 electron -1 no mass atomic 1

27 C e N Beta Decay 14 6 14 -1 7 Step 3: Write the beta particle.
Example 1: Write the nuclear equation for the radioactive decay of carbon – 14 by beta emission. Step 3: Write the beta particle. Step 4: Determine the other product (ensuring everything is balanced). Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # 14 C 6 14 e -1 N 7 Atomic #

28 Zr e Nb Beta Decay 97 40 97 -1 41 Step 3: Write the beta particle.
Example 2: Write the nuclear equation for the radioactive decay of zirconium – 97 by beta decay. Step 3: Write the beta particle. Step 4: Determine the other product (ensuring everything is balanced). Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # 97 Zr 40 97 e -1 Nb 41 Atomic #

29 electromagnetic γ no mass atomic always no omitted Gamma decay
Gamma rays – high-energy radiation, denoted by the symbol γ has no mass ( ) and no charge ( ). Thus, it causes change in or numbers. Gamma rays almost accompany alpha and beta radiation. However, since there is effect on mass number or atomic number, they are usually from nuclear equations. γ no mass atomic always no omitted

30 Transmutation conversion
the of an atom of one element to an atom of a different element. Radioactive decay is one way that this occurs! conversion

31 Type of Radioactive Decay
Review Type of Radioactive Decay Particle Emitted Change in Mass # Change in Atomic # Alpha α He -4 -2 Beta β e +1 Gamma γ 4 2 -1

32 half Half-life time Half-Life
is the required for of a radioisotope’s nuclei to decay into its products. For any radioisotope, # of ½ lives % Remaining 100% 1 50% 2 25% 3 12.5% 4 6.25% 5 3.125% 6 1.5625%

33 Half-Life

34 Half-Life For example, suppose you have 10.0 grams of strontium – 90, which has a half life of 29 years. How much will be remaining after x number of years?   You can use a table: # of ½ lives Time (Years) Amount Remaining (g) 10 1 29 5 2 58 2.5 3 87 1.25 4 116 0.625

35 initial mass mt = m0 x (0.5)n mass remaining # of half-lives
Half-Life Or an equation! initial mass mt = m0 x (0.5)n mass remaining # of half-lives

36 Half-Life Example 1: If gallium – 68 has a half-life of minutes, how much of a mg sample is left after 1 half life? ________ 2 half lives? __________ 3 half lives? __________

37 Half-Life Example 2: Cobalt – 60, with a half-life of 5 years, is used in cancer radiation treatments. If a hospital purchases a supply of 30.0 g, how much would be left after 15 years? ______________

38 Half-Life Example 3: Iron-59 is used in medicine to diagnose blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a mg sample will remain after days? ______________

39 Half-Life Example 4: The half-life of polonium-218 is 3.0 minutes. If you start with 20.0 g, how long will it take before only 1.25 g remains? ______________

40 Half-Life Example 5: A sample initially contains mg of radon After 11.4 days, the sample contains mg of radon Calculate the half-life.

41 changed nucleus Large energy
Nuclear Reactions Characteristics: Isotopes of one element are into isotopes of another element Contents of the change amounts of are released changed nucleus Large energy

42 Types of Nuclear Reactions
decay – alpha and beta particles and gamma ray emission Nuclear emission of a or Radioactive disintegration proton neutron

43 Fission splitting two equal Chain split slowly nuclear reactors speed
Nuclear Fission Fission splitting of a nucleus - Very heavy nucleus is split into approximately fragments reaction releases several neutrons which more nuclei - If controlled, energy is released (like in ) Reaction control depends on reducing the of the neutrons (increases the reaction rate) and extra neutrons ( creases the reaction rate). two equal Chain split slowly nuclear reactors speed absorbing de

44 Nuclear Fission - 1st controlled nuclear reaction in December st uncontrolled nuclear explosion occurred July - Examples – atomic bomb, current nuclear power plants

45 Nuclear Fission Disadvantages Advantages
Produces high level radioactive waste that must be stored for 10,000’s of years. Meltdown causes disasters like in Japan and Chernobyl. Advantages Zero air pollution Not a fossil fuel so doesn’t contribute to climate change

46 Nuclear Fusion - Fusion: Combining of two nuclei
- Two light nuclei combine to form a single heavier nucleus - Does not occur under standard conditions (positive nuclei repel each other) - Advantages compared to fission – No radioactive waste, inexpensive , - Disadvantages - requires large amount of energy to start, difficult to control. - Examples – energy output of stars, hydrogen bomb, future nuclear power plants

47 Uses of Radiation Radioactive dating: Carbon–14 used to determine the age of an object that was once alive. Detection of diseases: Iodine–131 used to detect thyroid problems, technetium–99 used to detect cancerous tumors and brain disorders, phosphorus – 32 used to detect stomach cancer. Treatment of some malignant tumors (cobalt–60 and cesium–137) cancer cells are more sensitive to radiation than normal, healthy cells

48 Uses of Radiation X-rays
Radioactive tracers: used in research to tag chemicals to follow in living organisms Everyday items: thorium–232 used in lantern mantels, plutonium–238 used in long-lasting batteries for space, and americium–241 in smoke detectors.


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